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Human Molecular Genetics Advance Access published online on February 5, 2008
Human Molecular Genetics, doi:10.1093/hmg/ddn019
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Dnmt1 Deficiency Promotes CAG Repeat Expansion in the Mouse Germline

Vincent Dion1, Yunfu Lin1, Leroy Hubert, Jr.1, Robert A. Waterland2 and John H. Wilson1,*

1 Verna and Marrs McLean Department of Biochemistry and Molecular Biology 2 Department of Pediatrics, USDA Children's Nutrition Research Center Baylor College of Medicine One Baylor Plaza Houston, TX, USA 77030

* Corresponding author: John H. Wilson, PhD Distinguished Service Professor Department of Biochemistry & Molecular Biology Baylor College of Medicine One Baylor Plaza Houston, TX 77030 Phone: 713 798-5760 Email: jwilson{at}bcm.tmc.edu

Received October 25, 2007; Revised January 15, 2008; Accepted January 15, 2008

Expanded CAG repeat tracts are the cause of at least a dozen neurodegenerative disorders. In humans, long CAG repeats tend to expand during transmissions from parent to offspring, leading to an earlier age of disease onset and more severe symptoms in subsequent generations. Here, we show that the maintenance DNA methyltransferase Dnmt1, which preserves the patterns of CpG methylation, plays a key role in CAG repeat instability in human cells and in the male and female mouse germlines. SiRNA knockdown of Dnmt1 in human cells destabilized CAG triplet repeats, and Dnmt1 deficiency in mice promoted intergenerational expansion of CAG repeats at the murine spinocerebellar ataxia type 1 (Sca1) locus. Importantly, Dnmt1+/– SCA1 mice, unlike their Dnmt1+/+ SCA1 counterparts, closely reproduced the intergenerational instability patterns observed in human SCA1 patients. In addition, we found aberrant DNA and histone methylation at sites within the CpG island that abuts the expanded repeat tract in Dnmt1-deficient mice. These studies suggest that local chromatin structure may play a role in triplet repeat instability. These results are consistent with normal epigenetic changes during germline development contributing to intergenerational instability of CAG repeats in mice and in humans.


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